for this shot, with the settings available on a DSLR, i'd definitely use aperture mode to control depth of field. set up on a tripod, or at the very least a sturdy brace, and close down the aperture to f8 or f11 at the least. that will let you keep the whole flower in focus, or nearly so. you'll lose some shutter speed by doing that, of course, and if this shot was 1/125, you'll probably drop down into the 1/60 or perhaps 1/30 range when you stop down to f8 or f11. at that point, you'll definitelt benefit from either a tripod or a solid brace, unless you're exceptionally steady.

the composition suggestions don't require any changes in settings, of course, but depending on how that affects your light, you may find you need to adjust other settings, such as ISO.